MAGELLAN OBSERVATIONS OF THE VENERA AND VEGA LANDING SITE REGIONS

Geologic maps have been produced for each of the seven Venera/Vega lan ding sites on Venus. The dominant terrain identified at all the sites is plains. The sites contain minor amounts of complex ridge terrain (C RT). complex terrain (CT), and an older plains (P(o)) that are all emb ayed by younger plains (P(y)). Some of the sites (Venera 9 and Vega 1 and 2) are made up of vast regional plains units while the other sites (Venera 8, 10, 13, and 14) contain more localized plains. The Venera 8 and 13 sites have unusual volcanic features associated with them and a nontholeiitic composition was measured by the landers at these site s. At the other five sites where a tholeiitic composition was measured , lava flows with morphologies that suggest an apparent low viscosity have been identified. This indicates a good correspondence between the geochemistry measured by the landers and the Magellan imagery. A good correlation also exists between the TV panoramas taken by four of the landers and the Magellan imagery. At the Venera 9, 10, 14 and Vega 1, 2 sites, the most likely material sampled are plains composed of thol eiitic lavas. A steep-sided dome, lamprophyre-like lavas, or ash beds are the most likely material sampled by the Venera 8 lander. The Vener a 13 lander may have sampled lava flows from a corona-like feature or from a steep-sided dome in the southeast of the landing circle. Radiop hysical properties of the landing sites show a good correspondence wit h the local geology, with most variations in backscatter, emissivity, and rms slopes reflecting differences in surface roughness. The Venera /Vega sites are good examples of typical venusian plains, indicating t hat geochemical measurements and TV observations provide representativ e characteristics of this most abundant terrain type on Venus.